Continuous process and system of producing polyether polyols

ABSTRACT

A continuous process and system for producing polyether polyols that allows for continuously adding an unreacted oxide to a loop reactor while adding at least one thermally deactivating catalyst capable of thermally deactivating prior to decomposition of polyether polyol which can allow for greater concentrations of unreacted oxides and/or a rate of reaction in the loop reactor is at a rate at least two times faster than a rate of reaction in a loop reactor containing less than 14 weight percent unreacted oxide. In a preferred embodiment, the catalyst is a double metal cyanide catalyst and a plug flow reactor is formed in series with the loop reactor wherein neither reactor contains a vapor space.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of the U.S.application Ser. No. 10/545,661, filed on Aug. 15, 2005, entitled“CONTINUOUS PROCESS AND SYSTEM OF PRODUCING POLYETHER POLYOLS,” theteachings of which are incorporated by reference herein, as ifreproduced in full hereinbelow, which claims priority from the U.S.Provisional Application No. 60/453,073, filed on Mar. 7, 2003, entitled“CONTINUOUS PROCESS AND SYSTEM OF PRODUCING POLYETHER POLYOLS,” theteachings of which are incorporated by reference herein, as ifreproduced in full hereinbelow.

FIELD OF THE INVENTION

This invention relates to the process and systems for the preparation ofpolyether polyols.

BACKGROUND OF THE INVENTION

Polyether polyols are used in the preparation of polyurethanes. Thesepolyethers are commonly prepared by polymerizing one or more alkyleneoxides in the presence of an initiator compound and a catalyst.

Polyethers are prepared in large commercial quantities through thepolymerization of these alkylene oxides such as propylene oxide andethylene oxide. The initiator compound usually determines thefunctionality (number of hydroxyl groups per molecule) of the polymerand in some instances incorporates some desired functional groups intothe product. The catalyst is used to provide an economical rate ofpolymerization and/or control product quality.

Historically, basic metal hydroxides or salts, such as potassiumhydroxide, were used as a catalyst. Polyether polyols are typically madein semi-batch reactors. Potassium hydroxide has the advantages of beinginexpensive, adaptable to the polymerization of various alkylene oxides,and easily recoverable from the product polyether.

It is furthermore known to use multimetal cyanide compounds, inparticular zinc hexacyanometallates, as catalysts. These complexesinclude compounds often referred to as multimetal cyanide or doublemetal cyanide (DMC) catalysts. These compounds are the subject of anumber of patents. Those patents include U.S. Pat. Nos. 3,278,457,3,278,458, 3,278,459, 3,404,109, 3,427,256, 3,427,334, 3,427,335,5,470,813, 5,482,908, 5,563,221, 5,689,012, 5,731,407, 5,770,678,5,771,177, 5,789,626, 6,018,017, 6,204,357, and 6,303,533. In someinstances, these metal cyanide complexes provide the benefit of fastpolymerization rates and narrow polydispersities.

The composition of these catalysts can vary widely, but can generally berepresented by the formula:

M_(b)[M¹(CN)_(r)(X)_(t) ].zL.aH₂O·nM_(x)A_(y)

-   -   wherein M is a metal ion that forms an insoluble precipitate        with the metal cyanide grouping M¹(CN)_(r)(X)_(t) and which has        at least one water soluble salt;    -   M¹ is a transition metal ion;    -   X represents a group other than cyanide that coordinates with        the M¹ ion;    -   L represents an organic complexing agent;    -   A represents an anion that forms a water-soluble salt with M        ion;    -   b and c are numbers that reflect an electrostatically neutral        complex;    -   r is from 4 to 6; t is from 0 to 2; and    -   z, n and a are positive numbers (which may be fractions)        indicating the relative quantities of the complexing agent,        water molecules and M_(x)A_(y) respectively.

One of the most common of these metal cyanide complexes is zinchexacyanocobaltate. Together with the proper complexing agent and anamount of a poly(propylene oxide), it has the advantages of beingactive. In the prior art, polyether polyols were prepared in batchprocesses. In these, the catalyst is suspended in the initiator. Whenthe reaction is complete, the catalyst must be separated from the finalproduct. Therefore, a need exists to provide a process and system toproduce polyether polyols in a continuous fashion.

The art such as Laid Open Japanese Patent Application KOKAI No. Hei6-16806 disclosed continuous reactors with double metal cyanidecatalysts that were backmixed reactors. It disclosed that the molecularweight distribution of the product using alkali catalysts was too high,but with double metal cyanide catalysts, the molecular weightdistribution was acceptable. Processes using double metal cyanidecatalysts have been shown effective in continuous processes such as seenin U.S. Pat. Nos. 5,689,012, 5,470,813, and 5,482,908. However, thesereferences rely on stirred tank reactors and/or plug flow reactorswherein the unreacted oxide was not maintained at a steady state.

Of note, U.S. Pat. No. 3,829,505 discloses that the propagation step ofthis reaction is exothermic and that some monomers may telomerize veryrapidly in the presence of the conventional DMC catalyst. This may becontrolled by the choice of the concentration of the catalyst, by use ofa diluent, and by the proper choice of temperature. This patent fails todisclose or teach the benefits of the use of unreacted oxide to controlreaction rate. Moreover, this patent fails to disclose or teach the useof a loop reactor in series with a plug flow reactor. Furthermore, thisreference neither teaches the effect of oxide concentration, nor optimaltemperature due to deactivation of catalyst.

For economic implementation of double metal cyanide catalysts andcontinuous reactor for large commodity polyols, the cost and usage levelof the catalyst is important to minimize. Typically backmixed reactorsrequire a higher level of catalysis than a plug flow reactor. Forexample, U.S. Pat. No. 5,767,323 disclosed double metal cyanidecatalysis that were higher in activity than conventional double metalcyanide catalysts, ultimately disclosing an “Exceptionally Active DMC”catalyst. These catalysts were claimed to achieve less than 15 ppmcatalyst level. This thermally stable double metal cyanide catalyst wasmost preferably stable at temperatures of 150° C. to 160° C. Higherreactor temperatures were preferred.

It is common practice to operate reactors polymerizing oxides with acontrolled amount of oxide present. For safety reasons, the reactors areoperated below a specified unreacted oxide concentration such that if aloss of cooling situation occurs, the adiabatic temperature rise of thereaction mixture does not approach the temperature at which thepolyether rapidly decomposes, which is greater than 250° C. as shown inGustin, Jean-Louis, The Process, Its Safety and the Environment—GettingIt Right, Institution of Chemical Engineers Symposium (200) Safety ofEthoxylation Reactions, 147 Hazards XV.

Notably, Dow's Fire & Explosion Index Hazard Classification Guide1987-published via the American Institute of Chemical Engineers inAppendix B Example problem 4 on page 58 suggests that 15 percentunreacted propylene oxide is a “worst case reaction mixture” for apolyol batch process reactor operating at a maximum reaction temperatureof 120° C. For potassium hydroxide reactions, neutralization of thereaction has been proposed as shown in Gotoh and Andoh, Chemical Stopperfor runaway propoxylation, Nagoya Fact. Sanyo Chem, Ind., Ltd., Tohkai,Japan. Yukagaku (19993), 42(1), 17-20. Unfortunately the adiabatictemperature rise is so fast that emergency or secondary controls can notbe implemented fast enough to prevent a high pressure event.

Therefore, a need exists for a catalyst that deactivates at temperaturesabove the polymerization and temperatures below the decomposition of theconstituents. Additionally, a need exists to continuously producepolyether polyols using a thermally deactivating catalyst capable ofpreventing a runaway reaction.

SUMMARY OF THE INVENTION

Double metal cyanide catalysts or other thermally deactivated catalystsimprove the safety of reactors and allow for them to be operated athigher unreacted oxides concentrations. Catalysts that thermallydeactivate allow time for secondary or emergency backup methods, such asemergency cooling, reaction quench methods, and backup power, to beimplemented.

By employing a thermally deactivating catalyst for alkoxylation, safetyrestrictions associated with limiting oxide concentration may berelaxed. Typically polymerization catalysts have first order kineticswith respect to oxide concentration. Therefore, operating reactors athigh levels of unreacted oxides would lead to more advantageouskinetics, which would allow for either greater productivity or reducedcatalyst usage. Conventional double metal cyanide catalysts may be usedand would be preferred, because they are easier and cheaper to produceand operate at lower temperatures. It is possible that someexceptionally active cyanide catalysts may be too reactive and thesystems could be difficult to control or assure remaining below 250° C.

In a preferred embodiment, the continuous process of producing polyetherpolyol includes continuously adding an unreacted oxide to a loopreactor, while adding at least one thermally deactivating catalyst andat least one initiator to the loop reactor; and reacting at least aportion of the unreacted oxide to form polyether polyol, wherein thethermally deactivating catalyst is capable of thermally deactivatingprior to decomposition of the polyether polyol, and wherein theunreacted oxide in the loop reactor is more than about 14 weightpercent. In a preferred embodiment, the catalyst is a double metalcyanide catalyst that is mixed in a pumpable slurry of a carrier.

The unreacted oxide may be ethylene oxide, propylene oxide, butyleneoxide, and/or a mixture of ethylene oxide, propylene oxide, and butyleneoxide. Typically, the initiator is a monol or polyol of diverse MWor/and functionality. The process may be conducted under controlledpressure. Moreover, the unreacted oxide and polyether polyol may alsopass through a plug flow reactor. Preferably, the amount of unreactedoxide in the loop reactor is no more than about 20 weight percent and/orthe catalyst in the loop reactor is less than about 150 ppm. Thisprocess may allow for a rate of reaction in the loop reactor at a rateat least two times faster than a rate of reaction in a loop reactorcontaining less than 14 weight percent unreacted oxide.

The system for the continuous process of producing polyether polyolpreferably includes a loop reactor containing at least one thermallydeactivating catalyst and a plug flow reactor following the loop reactorwherein the loop reactor and the plug flow reactor do not contain avapor space. This system may also include at least one pump and/or atleast one heat exchanger in the loop reactor. In a preferred embodiment,the system includes a recycling loop capable of returning the loopreactor, a portion of the unreacted oxide from an oxide flash columnplaced after the plug flow reactor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph that shows the effect of a deactivating catalystduring an adiabatic exotherm with 20 percent by weight propylene oxideinitial concentration;

FIG. 2 is a graph that shows the effect of initial reaction temperatureon exotherm for a deactivating catalyst;

FIG. 3 shows that for a deactivating catalyst and a loop reactor thatthere is an optimal operation temperature depending on the residencetime for a given unreacted oxide concentration; and

FIG. 4 is a schematic for a loop reactor followed by a plug flowreactor.

Those skilled in the art will recognize that the figures shown hererepresent just one method of the invention. Accordingly, significantdeviations from the figures are considered to be within the scope of theinvention, and nothing herein shall be considered to limit the scope ofthe invention as depicted in the claims.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention relates to a continuous method of producing polyetherpolyols by reacting initiators, such as diols or polyols, with ethyleneoxide, propylene oxide, butylene oxide or mixtures thereof in thepresence of a coordination type catalyst, like a multimetal cyanidecomplex catalyst. The term “continuous” is herein defined as a processwherein at least one reagent is fed into at least one reactor while apolymeric product is removed simultaneously during at least part of thereaction process.

The concepts of the present invention show the inclusion of at least onecatalyst capable of thermally deactivating the reaction prior todecomposition of the polyether polyol. FIG. 1 shows a computersimulation of the adiabatic temperature rise during a loss of coolingsituation for conventional DMC versus potassium hydroxide (KOH) with 20percent unreacted oxide by weight. This shows that a significant amountof time is still available before emergency methods are required.Moreover, this graph displays the advantage of including a thermallydeactivating catalyst during an adiabatic exotherm with 20 percent byweight propylene oxide initial concentration. The advantages ofincluding a thermally deactivating catalyst are evident in that therapid decomposition temperature of polyether polyol is either notreached or it is reached in such a slow manner that measures may betaken to prevent decomposition.

The reaction is preferably performed in a loop reactor and preferably aplug flow reactor in series. Any unreacted oxides leaving the plug flowreactor can be converted in a subsequent digester vessel or stripped outin a vacuum flash column. In a most preferred embodiment, the oxides,and the initiator, preferably containing the catalyst in a pumpableslurry, are fed into the loop reactor using a dosing system design.

Because heat transfer during propagation and transfer may be critical inmedium and large size batch reactors, loop type reactors can be used toreduce the induction period by temperature cycling in the loop, for theproduct is a liquid or semiliquid. Also, continuous telomerizationsystems may be used in which the telogen or monomer is fed into thesystem and polymer withdrawn.

Though these concepts are illustrated throughout with respect to a loopreactor and preferably a plug flow reactor in series, these inventiveconcepts of using a deactivating catalyst at higher unreacted oxideconcentrations can be used for semi-batch operation. A determination ofthe amount of unreacted oxide during the semi-batch operation is notclearly defined in the prior art. However, for the semi-batch reactors,the prior art relied upon propylene oxide to activate the catalyst witha certain amount of propylene oxide in an initiator. Typically theamount is 12 percent by weight to 14 percent by weight propylene oxideand then the pressure drops. The concepts as present in the presentapplication are capable of maintaining the pressure below a certainrange.

In a preferred embodiment, the loop reactor includes at least one heatexchanger in series and at least one circulation pump. The loop reactoreffluent leaves the loop reactor after the circulation pump and is fedinto the plug flow reactor. The reagents are fed into the loop reactorsystem after the loop reactor effluent point in the preferredembodiment.

A static or dynamic mixing device may be installed to mix thecirculating flow in the loop reactor with the reactor feed streams. Theactual loop reactor circulation flow rate is a trade-off betweenconditions required for efficient heat removal in the heat exchangers,pressure drop/pump energy requirements over the loop reactor, and mixingrequirements. Preferably, the heat exchangers are of the shell and tubetype with the coolant on the tube side for efficient heat transfer.However, those skilled in the art will recognize that other more compactconfigurations are applicable for use with the present invention.

In the preferred embodiment, the plug flow reactor is designed as ajacketed pipe with coolant inside the jacket. The process side, insidethe pipe, is preferably equipped with static mixer elements to enhanceplug flow conditions.

The digester vessel is preferably a normal pressure vessel withsufficient residence time to convert the unreacted oxides to below amaximum allowable level as specified by product quality requirements.Alternatively, the unreacted oxide is removed by vacuum and temperature,such as applied at a falling film evaporator with or without the help ofstripping agents such as c nitrogen added counter-currently.

This system allows for continuous operation and liquid full capacity.This allows for the operation of the vessels without a vapor space. Bydoing so, the operating constraints as determined by the process safetyrequirements of the prior art are overcome. The potentially explosivecompositions that may exist in a vapor space of the vessels of the priorart cannot exist in the present invention.

FIG. 2 shows the effect of polymerization temperature on the adiabatictemperature rise. This graph shows the effect of initial reactiontemperature on exotherm for a thermally deactivating catalyst. Thisshows that from a safety perspective it would be beneficial to operateat lower temperatures than higher temperatures at the same oxideconcentration. As a result, it is possible to operate the system athigher unreacted oxides also referred to as unconverted oxideconcentrations. Higher unreacted oxides allow for faster activation ofcatalysts and higher reaction rates at lower catalyst concentrations.

FIG. 3 is a graph that shows the optimum reaction temperature fordifferent values of residence time in a continuous reactor when athermally deactivating catalyst is used. At 110° C., for example, thereactor with a residence time of 1 hour has a polymerization rate thatis twice the rate of the same reactor at 135° C. Operating the reactorat the optimum temperature is thus desirable since, for a givenpolymerization rate, this type of operation allows lower catalyst andlower unconverted oxide concentrations.

The optimum reaction temperature is the result of two opposingmechanisms whose rates increase with temperature. One mechanism is thedeactivation of the catalyst and the other is the chain growthmechanism. At low temperatures, the rate of catalyst deactivation isslow but so is the rate of chain growth. At high temperatures, chaingrowth should be faster but the overall process is slow because thecatalyst has lost most of its activity. High reactor residence timesallow more catalyst deactivation, giving lower polymerization rates atthe optimum temperature.

Notably, the coordination catalyst is important to this type ofreaction. By using a loop reactor as the primary reactor, the reagentstreams are immediately exposed to active catalyst already present inthe loop reactor, due to the back mixing nature of the system. Becauseof the residence time in the entire system, the catalyst has sufficienttime to activate at reactions conditions either in the loop reactor orin the loop reactor and plug flow reactor combination.

Moreover, the heat transfer capability of the reactor system is usuallythe overall limiting factor as to the overall production rate, becauseof the polyol viscosity at the heat exchanger wall and the totalinstalled heat transfer area. In the loop reactor, most of the reactorvolume is in the heat exchanger by design where coolant temperaturedifferences are relatively small. Therefore, the polyol viscosityeffects near the heat exchanger wall on the heat transfer rate arenegligible, and the installed heat transfer area is so large that thesystem may be reaction rate constrained instead of heat transferlimited.

Furthermore, the reactor system is less reaction rate constrained byusing coordination catalyst that have improved characteristics. In thepreferred embodiment, the thermally deactivating property of thiscatalyst may allow for the catalyst to aid in the control of thereaction rate. This thermally deactivating property may allow thecatalyst to effectively prevent the thermal decomposition of thecontents of the loop reactor and/or the plug flow reactor, thusinhibiting the rupturing of at least one of these reactors.

Additionally, the use of these types of catalysts allow forcustomization of the design of the system. The system may therefore bedesigned in light of reagent feed systems, reactor systems such as aloop reactor in series with a plug flow reactor, product storage as theplug flow reactor effluent will be at product specifications, andadditional factors or combinations of the above.

An improved safety alkoxylation reactor design was developed based onthe loop reactor design followed by a plug flow reactor as shown in FIG.4. This design is particularly effective for use with reactions havinghighly exothermic kinetics.

The loop reactor 10 may include a recycle pump 12, heat exchanger(s) 14,raw material inputs 16 a and/or 16 b, product take off 18 and a controlsystem 20. The loop reactor 10 preferably operates at a controlledpressure that is dictated by the reactor temperature and unreacted oxideconcentration. The product take off 18 then goes to a plug flow reactor22 to digest or complete the reaction of the unreacted oxide. Thecatalyst is preferably added as a pumpable slurry in an initiatormaterial. Propylene oxide 16 c and ethylene oxide 16 d may be fed aswell into the loop reactor 10.

The loop reactor is specifically operated without a vapor space in theloop reactor. This offers an additional safety advantage with handlingoxides. Vapor space concentration of ethylene oxide typically needs tobe controlled in semi-batch reactors to avoid explosion conditions andthe reduction or elimination of a vapor space is an enhancing feature ofthe loop reactor design. The elimination of the vapor space also helpseliminate the potential for gel formation associated with the use of DMCcatalysts. Sticky polyol gels tend to form in reactors using DMCcatalysts, and these gels tend to accumulate over time, fouling thereactor and eventually forcing a shutdown.

The loop reactor can also be operated at different recycle/feed flowratios which allows the reactor to be operated like a completelybackmixed reactor or as a moderately backmixed reactor. This is anadvantage over the prior art in that the rate of the reaction ratherthan the temperature may control the output of the system.

The product polymer may have various uses, depending on its molecularweight, equivalent weight, functionality and the presence of anyfunctional groups. Polyether polyols that are made are useful as rawmaterials for making polyurethanes. Polyether polyols can also be usedas surfactants, hydraulic fluids, as raw materials for makingsurfactants and as starting materials for making aminated polyethers,among other uses.

The catalyst is preferably complexed with an organic complexing agent. Agreat number of complexing agents are potentially useful, althoughcatalyst activity may vary according to the selection of a particularcomplexing agent. Examples of such complexing agents include alcohols,aldehydes, ketones, ethers, amides, nitriles, and sulfides. In apreferred embodiment, the catalyst is a double metal cyanide.

Suitable polyols include polyethers based on ethylene oxide (EO),propylene oxide (PO), butylene oxide (BO), and random or block mixturesthereof. Low molecular weight polyether polyols, particular those havingan equivalent weight of 350 or less, more preferably 125-250, are alsouseful complexing agents.

For making high molecular weight monofunctional polyethers, it is notnecessary to include an initiator compound. However, to controlmolecular weight and molecular weight distribution impart a desiredfunctionality (number of hydroxyl groups/molecule) or a desiredfunctional group, an initiator compound is preferably mixed with thecatalyst complex at the beginning of the reaction. Suitable initiatorcompounds include monols and monoalcolaols such methanol, ethanol,n-propanol, isopropanol, n-butanol, isobutanol, tbutanol, octanol,octadecanol, 3-butyn-1-ol, 3-butene-1-ol, propargyl alcohol,2-methyl-2-propanol, 2-methyl-3-butyn-2-ol, 2-methyl-3-butene-2-ol,3-butyn-1-ol, and 2-butene-1-ol. Suitable monoalcohol initiatorcompounds include halogenated alcohols such as 2-chloroethanol,2-bromoethanol, 2-chloro-1-propanol, 3-chloro-1-propanol,3-bromo-1-propanol, 1,3-dichloro-2-propanol,1-chloro-2-methyl-2-propanol and 1-t-butoxy-2-propanol as well asnitroalcohols, keto-alcohols, ester-alcohols, cyanoalcohols, and otherinertly substituted alcohols. Suitable polyalcohol initiators includeethylene glycol, propylene glycol, glycerine, 1,1,1-trimethylol propane,1,1,1-trimethylol ethane, 1,2,3-trihydroxybutane, pentaerythritol,xylitol, arabitol, mannitol, 2,5-dimethyl-3-hexyn-2,5-diol,2,4,7,9-tetramethyl-5-decyne-4,7-diol sucrose, sorbitol, alkylglucosides such as methyl glucoside and ethyl glucoside, mixturesthereof.

The following examples are provided to illustrate the invention, but arenot intended to limit its scope. All parts and percentages are by weightunless otherwise indicated.

EXAMPLES

DMC was prepared from methanolic H₃Co(CN)₆ (3.00 mmol, 7.70 wt percent(max) in MeOH, 1.76 meq H⁺/g solution), ZnO (6.0 mmol), andtrimethylolpropane in methanol solvent. VORANOL® polyol 2070 (a glycerolpropoxylate triol with a formula weight of approximately 700 availablefrom The Dow Chemical Company) was subsequently added and the resultantDMC complex was devolatilized with methanol/water distillation. (VORANOLis a trademark of The Dow Chemical Company.) Approximately 2.00 wtpercent DMC/ZnSO₄ (Maximum) in 30:1 wt/wt VORANOL 2070polyol/trimethylolpropane. Notably, this preparation may use less ZnO,thus providing a slightly acidic slurry and was performed with a 2.33:1total Zn:Co ratio.

A methanolic solution of H₃Co(CN)₆ (8.50 g of 7.70 wt percent solution,approximately 2.7-3.0 mmol,) was added to an opaque, white slurry of ZnO(0.57 g, 7.0 mmol) and trimethylolpropane (1.87 g, 14 mmol) in methanol(40.0 g, 51 mL) dropwise via an addition funnel over 50 minutes withmoderate-rapid stirring (250 mL round-bottom stripping flask with 1 inchlong octagonal magnetic stir bar). The funnel was rinsed three timeswith 1½ mL of MeOH.

The ZnO appeared to slowly dissolve as the H₃Co(CN)₆ solution was added,simultaneously producing the DMC solid. The slurry was stirred for 20minutes after the H₃Co(CN)₆ addition was complete. The slurry (61.99 g,pH=3-4) was very stirrable and consisted of a very finely divided whiteDMC suspension in methanol/TMP. The DMC particles appeared to be veryfinely divided, with no apparent “large” particles. The pH may be testedby first removing a small sample of the slurry then diluting with anequal volume of water.

VORANOL polyol 2070 (56.0 g) was then added to the stirred methanolicDMC/TMP slurry. The slurry was stirred for 10 minutes after the VORANOLpolyol 2070 addition. The mass of the (pH=3-4) methanolic DMC/VORANOLpolyol 2070/TMP slurry was 117.99 g. The slurry may became moretranslucent when the VORANOL polyol 2070 was added.

The magnetic stir bar was then removed (with small methanol rinses) andthe volatiles (methanol) were distilled from the DMC slurry on arotoevaporator. The distillation of the bulk of the methanol solvent wasinitially performed at up to 50° C./25 inches Hg vacuum with amoderate-strong nitrogen sweep. The distillation was conducted underthese conditions (50° C./25 inches Hg vacuum) over 50 minutes, providinga translucent, white, highly dispersed slurry (mass=60.56 g, pH=3-4). Atthis point the vacuum was increased to 29-30 inches Hg vacuum (still 50C) with a moderate nitrogen sweep. After 60 minutes of devolatilizationat 50° C./29-30 inches Hg, the slurry (59.19 g, pH=3-4) was stilltranslucent, white, and highly dispersed.

The temperature and vacuum were increased to 75-80° C./30 inches and afinal finishing strip was performed for an additional 30 minutes at75-80° C./30 inches Hg (full pump vacuum) with a slight nitrogen sweep.The slurry remained translucent and white during the finishing strip at75-80° C., with no discoloration or darkening observed. No unreacted ZnOwas visible in the slurry. (NOTE: Minimal additional mass loss wasobserved in the final (75-80° C.) finishing strip.) The flask containingthe final highly dispersed, translucent, white DMC slurry (59.09,pH=3-4) was allowed to cool to room temperature under nitrogen then wascapped with a rubber septum. The flask was taken into a nitrogenatmosphere drybox and the moderate viscosity slurry was poured into astorage bottle.

Using the DMC catalyst, the reaction kinetics of the polymerization ofPO were developed using glycerine alkoxylates as initiators. From thosekinetics, a reaction model was established. The model was used to runoptimization experiments summarized below.

The reactor conditions are modeled with the following conditions shownin Table 1:

TABLE 1 Modeled Reaction Variable Value Monomer Feed Rate (g/s) 8.34Catalyst Slurry Feed Rate (g/s) 0.03 Fraction Catalyst in Feed Slurry(wt- 0.02 frac) Initiator Feed Rate (g/s) 2.0 Molecular Weight ofInitiator (g/mol) 700.0 CSTR Reactor Volume (l) 50.0 CSTR ReactorTemperature (C.) 110.0 Tubular Reactor Volume (l) 50.0 Tubular ReactorTemperature (C.) 125.0

The initiator is a 700 Mw triol. VORANOL polyol 2070 (56.0 g,approximately 80 mmol). The catalyst slurry feed rate (2 percent DMC ininitiator) is adjusted and the results are shown in the Table 2:

TABLE 2 Modeled Reaction for Example. Value Variable Monomer Feed Rate(g/s) 8.34 Catalyst Slurry Feed Rate (g/s) 0.025 Tubular Reactor Volume(l) 50 Result CSTR PO outlet conc. (wt percent) 9.7 PFR PO outlet conc.(ppm) 6841 Catalyst outlet conc. (ppm) 48.2A modeled reaction at a lower catalyst concentration is shown in Table3:

TABLE 3 Modeled Reaction for Example 2 - Lower Catalyst Conc. ValueVariable Monomer Feed Rate (g/s) 8.34 Catalyst Slurry Feed Rate (g/s)0.01 Tubular Reactor Volume (l) 150 Result CSTR PO outlet conc. (wtpercent) 15.2 PFR PO outlet conc. (ppm) 6300 Catalyst outlet conc. (ppm)19.3The model shows by increasing the unreacted oxide concentration setpointin the loop reactor from 10 to 15 percent, the catalyst concentrationwill be decreased by over 2 times. Turning to Table 4, a model is shownfor doubling the reactor output:

TABLE 4 Modeled Reaction for Example 3 - Double Reactor Output ValueVariable Monomer Feed Rate (g/s) 15 Catalyst Slurry Feed Rate (g/s) 0.02Initiator Feed (g/s) 4.0 Tubular Reactor Volume (l) 250 Result CSTR POoutlet conc. (wt percent) 19.5 PFR PO outlet conc. (ppm) 6380 Catalystoutlet conc. (ppm) 21

This example shows that continued increase in Loop reactor oxideconcentration to 20 percent from 15 percent would allow a doubling ofproductivity at the same catalyst concentration. In each case, where theoxide concentration in the loop reactor is increased, the volume of theplug flow reactor may be increased in order to maintain a reasonableoxide concentration.

Oxide that remains in the polyol after the reactor is stripped out ofthe polyol and recycled back to the reactor or propylene oxide plant.There is an economic optimal on the amount of propylene oxide to be leftin the polyol after the reactor.

In additional experiments, the reactor conditions are modeled with thefollowing conditions shown in Table 5:

TABLE 5 Modeled Reaction Variable Value Monomer Feed Rate (g/s) 8.34Catalyst Slurry Feed Rate (g/s) 0.07 Fraction Catalyst in Feed Slurry(wt- 0.02 frac) Initiator Feet Rate (g/s) 2.0 Molecular Weight ofInitiator (g/mol) 3000.0 CSTR Reactor Volume (l) 75.0 CSTR ReactorTemperature (C.) 100.0 Tubular Reactor Volume (l) 75.0 Tubular ReactorTemperature (C.) 105.0

The initiator is a 3000 Mw triol, VORANOL polyol 2070. The results areshown in Table 6:

TABLE 6 Modeled Reaction for Example 4. Value Variable Monomer Feed Rate(g/s) 8.34 Catalyst Slurry Feed Rate (g/s) 0.07 Tubular Reactor Volume(l) 75 Result CSTR PO outlet conc. (wt percent) 9.0 PFR PO outlet conc.(ppm) 6700 Catalyst outlet conc. (ppm) 134A modeled reaction at a lower catalyst concentration is shown in Table7:

TABLE 7 Modeled Reaction for Example 5 - Lower Catalyst Conc. ValueVariable Monomer Feed Rate (g/s) 8.34 Catalyst Slurry Feed Rate (g/s)0.035 Tubular Reactor Volume (l) 315 Result CSTR PO outlet conc. (wtpercent) 15.2 PFR PO outlet conc. (ppm) 6700 Catalyst outlet conc. (ppm)67The model shows that by increasing the unreacted oxide concentrationsetpoint in the loop reactor from 9 to 15 percent, the catalystconcentration will be decreased by over 2 times. Turning to Table 8, amodel is shown for doubling the reactor output:

TABLE 8 Modeled Reaction for Example 6 - Double Reactor Output ValueVariable Monomer Feed Rate (g/s) 16.68 Catalyst Slurry Feed Rate (g/s)0.07 Initiator Feed (g/s) 4.0 Tubular Reactor Volume (l) 650 Result CSTRPO outlet conc. (wt percent) 20.0 PFR PO outlet conc. (ppm) 6700Catalyst outlet conc. (ppm) 67This example shows that continued increase in Loop reactor oxideconcentration to 20 percent from 15 percent would allow a doubling ofproductivity at the same catalyst concentration. In each case, where theoxide concentration in the loop reactor is increased, the volume of theplug flow reactor may be increased in order to maintain a reasonableoxide concentration.

Based on the data obtained from the model simulations, production ofpolyol in a pilot plant are performed using a DMC catalyst as preparedabove. The initial set of pilot plant conditions are shown in Table 9:

TABLE 9 Basic Set of Pilot Plant Conditions - Example 7 Variable ValueMonomer Feed Rate (kg/hr) 10.3 Catalyst Slurry Feed Rate (g/hr) 50Catalyst in Feed Slurry (wt-fracation) 0.03 Initiator Feed Rate (kg/hr)2.1 Molecular Weight of Initiator (g/mol) 625 Loop Reactor ResidenceTime (hr) 5 Loop Reactor Temperature (C.) 94 Tubular Reactor ResidenceTime (hr) 5 Tubular Reactor Temperature (C.) 94

The initiator is a 625 Mw triol made from the KOH catalyst ethoxylationof glycerin. The potassium is removed via absorption on magnesiumsilicate to less than 5 ppm. The corresponding results are shown inTable 10:

TABLE 10 Results for Example 7. Value Variable Catalyst Slurry Feed Rate(g/hr) 50 Result Loop PO outlet conc. (wt percent) 3.9 Catalyst outletconc. (ppm) 121An experiment at a lower catalyst concentration is shown in Table 11:

TABLE 11 Results for Example 8 - Lower Catalyst Conc. Value VariableCatalyst Slurry Feed Rate (g/hr) 29 Result Loop PO outlet conc. (wtpercent) 14.4 Catalyst outlet conc. (ppm) 70These results show that by increasing the unreacted oxide concentrationsetpoint in the loop reactor from 3.9 to more than 14.4 percent, thecatalyst concentration is decreased by almost 40 percent. Turning toTable 12, results are shown for the case where process output increasesand catalyst concentration decreases when the unreacted oxide goes up:

TABLE 12 Operating Conditions and Results for Example 9 Value VariableLoop Reactor Residence Time (hr) 2 Loop Reactor Temperature (C.) 94Tubular Reactor Residence Time (hr) 4 Tubular Reactor Temperature (C.)94 Result Loop PO outlet conc. (wt percent) 16.7 Catalyst outlet conc.(ppm) 100

When compared to example 7, this example shows that increasing unreactedoxide concentration from 3.9 percent to 16.7 percent allows an increasein productivity by a factor of 2.5 and a reduction of almost 20 percentin catalyst concentration.

While only a few, preferred embodiments of the invention have beendescribed, those of ordinary skill in the art will recognize that theembodiment may be modified and altered without departing from thecentral spirit and scope of the invention. Thus, the preferredembodiments described above are to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the following claims, rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalents of the claims are intended to be embraced.

1. A system for the continuous process of producing polyether polyolcomprising: a loop reactor containing at least one thermallydeactivating catalyst; and a plug flow reactor following the loopreactor; wherein the loop reactor and the plug flow reactor do notcontain a vapor space.
 2. The system of claim 1, further comprising atleast one pump in the loop reactor.
 3. The system of claim 1, furthercomprising at least one heat exchanger in the loop reactor.
 4. Thesystem of claim 1, further comprising a recycling loop capable ofreturning a portion of the unreacted oxide from the plug flow reactor tothe loop reactor.